High fiber products are generally considered to be healthful foods and food ingredients. There are two basic types of fiber: soluble and insoluble. Soluble fiber is soluble in aqueous solutions while insoluble fiber is not. Insoluble fiber will improve regularity and bulk formation but may do very little to lower serum cholesterol. Indeed some studies indicate that, depending on the source, insoluble fiber may actually increase serum cholesterol. Soluble fiber has been strongly linked to regularity and cholesterol reduction, and less strongly to sugar regulation in diabetics and colon cancer prevention.
Soluble fiber is highly viscous when it goes into solution and this sticky material has the capacity to tie up cholesterol precursors such as bile salts, excess sugar, and other potential carcinogenic compounds and flush them out of the body as fecal material. The water holding capacity of this material has the effect of forming a softer, more efficiently moving stool and the viscosity of this material lubricates the intestines. This is an aid to people with intestinal wall weakness or sensitivity that results in intestinal bleeding. Unfortunately soluble fiber is currently associated with large amounts of harsh insoluble fiber in products such as oat bran concentrate. The harsh insoluble fiber in such products as oat bran concentrate can tear at the intestinal walls during passage, causing bleeding and thus negating the positive effect of the soluble fiber with which it coexists.
There are many forms of soluble fiber that are used as food ingredients, many are categorized as gums. Some examples of soluble fiber food ingredients or food components are guar gum, gum Arabic, carrageenin, pectin, psyllium, and beta glucan. Most of these products are relative expensive. Pectin is relatively less expensive, plentiful and is found in fruit pulp. However, pectins can set up a hard gel in the intestines and large amounts of this material can cause intestinal blockages.
Another soluble fiber is beta glucan, or beta 1-4/1-3 glucosyl pyranose polymer. Beta glucan occurs in two common grain cereals, oats and barley which contains 5-7% beta glucan and is present in the cell walls along with other forms of fiber such as cellulose and arabinoxylan. Between 20-70% of the beta glucan found in oats and barley is soluble in warm water at 45.degree. C. Cellulose, which is completely insoluble in warm water, is a straight chain of beta 1-4 linked glucose molecules. Beta glucan has the same beta 1-4 linkages but is staggered having beta 1-3 linkages after 4-6 beta 1-4 linkages. This results in a laminated macro-molecule. This general beta glucan structure will continue for 20,000 to 100,000 glucose units. The laminations allow water molecules to fit in between the beta 1-4 layers which allows beta glucan to hydrolyze.
Beta glucan occurs as fibers in the cell wall of the starchy endosperm in barley seed. Beta glucans coexist in the cell with preformed beta glucanases which are enzymes that break up beta glucan. Beta glucanases are released or activated as the seed is hydrated. Additionally as the seeds germinate, newly made beta glucanase is released from the scutellum and from the aleurone layer of the seed into the endosperm. Thus, as water is added to the seed, beta glucans are degraded and broken down into smaller units through the activity of beta glucanase. Additionally any excessive drying or dry heat will cause these beta glucan chains to break up, which in turn causes the all important function of viscosity to be lost.
Oats beta glucan, tends to be concentrated in the bran, which is the outer layer of the seed. When concentrated in oat bran fiber, the beta glucan is less than half the total fiber content with insoluble fiber being the major fiber component. Thus the harshness of the coarse bran fiber must be accepted along with the benefits of the soluble beta glucan. Additionally, oats does not have a large millable endosperm in which starch, protein, and other millable products can be stored.
However, barley is a millable grain and beta glucan is concentrated in the starchy endosperm, not in the bran layer. Thus, barley beta glucan in the endosperm cell walls can be concentrated without accumulating insoluble harsh bran fiber. Barley can be milled or pearled to remove harsh bran fiber and germs. Pearling has the additional advantage of reducing oil content, an unwanted component of any soluble fiber concentrate. In 1981 (Fox, G. J. Dissertation, Montana State University, 1981) Fox reported that a particular variant of barley, waxy hulless, contained unusually high levels of beta glucan activity measured as viscosity, showing 4.0-10.0 times that found in normal hulled barley. Viscosity was doubled when the short awn gene was added to produce waxy hulless short awn barley. Actual beta glucan content was found to be 1.5-2.0 times that of normal barley in waxy hulless and waxy hulless short awn barley (C. E. Fastnaught et al, Genetic and environmental variations in beta glucan content and quality parameters of barley for food, submitted for publication to Crop Sci., 1995). In the last 10 years a great deal of research has been concentrated toward the development of hypocholesterolaemic foods and food ingredients from oats and barley with special emphasis on the high beta glucan waxy hulless barley. One problem is that inconsistent results have arisen from clinical studies on the hypocholesterolaemic efficacy of the two beta glucan bearing grains, oats and barley. (R. K. Newman, et al., Cereal Chem. 69(3) 240-244, 1989; J. G. Fadel, et al., Nutr. Rep. Int., 35: 1049-1054, 1987). This inconsistency is due in part to the fact that the functional properties of the beta glucan are not directly related to it's content but to the viscosity that is produced in the intestines (S. Bengtsson, et al., J. Sci. Food Agric., 39: 151-161, 1990; T. S. Kahlon, et al., Cereal Chem., 70(4) 435-440, 1993; J. Raloff, Food Tech., August, 1991). Intestinal viscosity is also the basis for the sugar and fecal regulation associated with soluble fiber. In almost all clinical studies the beta glucan content of the starting material is determined but not the functionality (i.e. viscosity). It is possible to have material with high levels of beta glucan but zero functionality with viscosity less than 5 cps, (R. K. Newman, et al., Cereal Food Worlds, 34: 883-886, 1989; C. E. Fastnaught, et al., 1995).
Thus, previous efforts to concentrate clinically effective beta glucan have failed because there has been no effort to concentrate the true functional property of the beta glucan, which is viscosity.
Barley is somewhat unique in that it contains elevated levels of another cholesterol inhibitor, tocotrienol which is a vitamin E derivative that occurs in barley pearlings, and lowers serum cholesterol levels by interfering with the biosynthesis of cholesterol. This is a completely different mechanism for serum cholesterol reduction than that produced by soluble fiber.